In interstitial radiation therapy, one method for treating tumors is to permanently place small, radioactive seeds into the tumor site. This method is currently accomplished by one of the following two procedures: (a) loose seeds are implanted/placed in the target tissue. The loose seeds, however, are dependent on the tissue itself to hold each individual seed in place during treatment; and (b) seeds are contained within a woven or braided absorbable carrier such as braided suture material.
Currently, the commercially available carrier materials are soft, essentially deflecting materials intended to be pulled through the tissue as opposed to being pushed through the material. The carrier with the seeds disposed therein is secured in place as a single unit, as opposed to one or more individual seeds being held in place, with the plurality of the seeds being held together in the target tissue.
To minimize radiation during handling and shipping, the carrier material with the radioactive seeds therein has been shielded by placing the carrier material and seeds in a curved stainless steel metallic tube ring which attenuates more than 99.9% of the I-125 photons. See U.S. Pat. No. 4,697,575 and European Patent Publication Number 0064,860 published 17.11.82, Bulletin 82/46.
What is desired in using an elongated material having radioactive seeds spaced throughout the material is that the material be sufficiently rigid as to be "non-deflecting." "Non-deflecting" is defined as meaning a delivery system comprising an elongated material, which is absorbable in the living tissue, and having spaced radioactive seeds disposed therein, which has sufficient rigidity to be inserted into a living body near or into a tumor without substantial deflection of the elongated material to provide controlled and precise placement of the radioactive seed material.
While semi-rigid bio-absorbable materials with spaced radioactive seeds are known for use as interstitial implants, they are not entirely satisfactory for relatively large-scale commercial operations. In one instance, the elongated material was made using a bio-absorbable material made of an Ethicon Vicryl.RTM. material. Radioactive seeds and teflon spacers were inserted into the material. Needles loaded with the seeds in the carrier material were sterilized or autoclaved causing contraction of the carrier material resulting in a rigid column of seeds and spacers. "Ultrasonically Guided Transperineal Seed Implantation of the Prostate: Modification of the Technique and Qualitative Assessment of Implants" by Van't Riet, et al., International Journal of Radiation Oncology, Biology and Physics, Vol. 24, No. 3, pp. 555-558, 1992.
Another system for providing a semi-rigid elongated material having radioactive seeds disposed therein is disclosed in U.S. Pat. No. 4,697,575 in which a plurality of capsules formed of encapsulated radioactive seeds are positioned in a predetermined array. The seeds are formed into individual, encapsulated capsules, each capsule having a projection on one capsule end and a complementary recess on the remaining capsule end. A projection in one capsule is engageable with a recess in an adjacent capsule such that the desired number of seeds can be plugged together to form a column of rigid bio-absorbable elongated material. This system is not entirely satisfactory inasmuch as it is time consuming to carry out the manipulative plugging steps in assembling a strand of elongated material. One feature desired for a semi-rigid strand is that it be assembled relatively easily and efficiently.
Another feature which is particularly important and desired in providing a semi-rigid bio-absorbable material and seeds is that the radioactive seeds be maintained at a fixed and controlled center-to-center spacing between seeds. It has been found that, in some instances, maintaining the proper spacing between seeds is not always achieved.
What is desired is to provide a semi-rigid bio-absorbable carrier material having seeds disposed within the material with the seeds being accurately spaced a predetermined distance from one another, e.g., 1 centimeter center to center. It is further desired to be able to manufacture the semi-rigid seed carrier in an efficient and relatively expeditious manner to avoid time consuming process steps.
Moreover, it is desired to transport the semi-rigid seed carrier, as a sterile unit, from the manufacturer directly to the site of use in a manner that the carrier is not contaminated by foreign objects and the carrier can be removed from an assembly in a relatively easy manner.